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Instruments / Technical Area	Publication Details	Published
B16-Test Beamline B18-Core EXAFS Optics	Swelling of steel film by hydrogen absorption at cathodic potential in electrolyte Debi Garai , Ilaria Carlomagno , Vladyslav Solokha , Axel Wilson , Carlo Meneghini , Christian Morawe , Vadim Murzin , Ajay Gupta , Jorg Zegenhagen Physica Status Solidi (b) 3 DOI: 10.1002/pssb.202000055 Open Access Show Abstract ▼ Abstract: An ≈4 nm FeCrNi film, deposited on a Ru/B4C multilayer (ML), is used to study cathodic hydrogen charging in electrolyte. A thin film on a ML allows obtaining precise quantitative information on surface metal composition and oxidation state using the X‐ray standing wave technique combined with near‐edge X‐ray absorption spectroscopy. The metal composition is found being close to the composition of stainless steel (SS) 304, and, as for bulk steel, the outer 2 nm passive layer, consisting of oxidized iron and chromium, is depleted of nickel. Overall, it is found that the film represented a useful replica of the surface of bulk steel. Following exposure to 0.1 m KCl electrolyte at −0.6 V versus Ag/AgCl, 11.3 (±3)% swelling of the film by hydrogen absorption is observed. The estimated absorbed amount is exceeding reported bulk absorption under similar conditions by more than an order of magnitude. Strong hydrogen absorption appears to be enabled by the 2D character of the thin film, i.e., a significantly lower associated strain energy compared with bulk absorption. The strong surface swelling is suggested to be related to the lowering of the pitting corrosion resistance of SS surfaces reported following hydrogen exposure.	Apr 2020
B16-Test Beamline B18-Core EXAFS I08-Scanning X-ray Microscopy beamline (SXM)	Studying the onset of galvanic steel corrosion in situ using thin films: film preparation, characterization and application to pitting Debi Garai , Vladyslav Solokha , Axel Wilson , Ilaria Carlomagno , Ajay Gupta , Mukul Gupta , V. R. Reddy , Carlo Meneghini , Francesco Carla , Christian Morawe , Jorg Zegenhagen Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/abd523 Diamond Proposal Number(s): [17145] Open Access Show Abstract ▼ Abstract: This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron X-radiation. Characterized by X-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈ 4 nm thickness were studied in situ in an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by X-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at ≈ +0.8 V Cr-oxide was removed from the film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by X-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft X-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.	Dec 2020
I08-Scanning X-ray Microscopy beamline (SXM)	Soft X-ray spectromicroscopic evidence for site-specific nanoscale phase segregation of polyurethane onto a confined surface Kavita Sharma , Debi Garai , Ajay Gupta , Debmalya Roy , N. Eswara Prasad The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.1c06052 Diamond Proposal Number(s): [24782] Show Abstract ▼ Abstract: Synchrotron-based small-angle X-ray scattering and near-edge X-ray absorption fine structure spectromicroscopy have been used to study the phase separation of thermoplastic polyurethane in a confined thin-film geometry. The functional nanomaterials were introduced in a polymer matrix, where the shape and nature of the functional surface were varied to gain insight into the mechanism of aggregation of polyurethane segments enriched with functional moieties. Using soft X-ray scattering it has been established that the two-dimensional flat functional surface displayed higher phase-segregated geometries with a wider distribution of interdomain spacing in comparison to the one-dimensional contour shaped nanofillers. A strong chemical environment dependence has been observed for π–π or electrostatic interactions during the nanoscale phase separation of the polyurethane matrix by X-ray absorption spectromicroscopy. Our results support the fact that soft X-ray-based spectromicroscopy can be exclusively used as a powerful noninvasive technique for the structure–property analysis of polymer nanocomposites.	Sep 2021

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